Currently, with the emergence of the services such as Video on Demand (VOD), High-Definition Television (HDTV) and online gaming, telecom users raise higher and higher requirements on network bandwidth. Driven by such requirements, the Fiber to the Home (FTTH) technology that ensures the “last mile” access network is developing rapidly, and especially, the PON technology is applied widely.
FIG. 1 shows a structure of a traditional PON system. A traditional PON system is composed of an Optical Line Terminal (OLT), more than one Optical Network Unit (ONU), and an Optical Distribution Network (ODN) that connects the ONU to the OLT. The ODN includes a passive optical splitter for distributing optical power, a feed fiber between the passive optical splitter and the OLT, and a branch fiber between the passive optical splitter and the ONU. In a traditional PON system, the OLT covers the ONUs that are not over 20 km away.
Monitoring and maintenance of a traditional PON system are illustrated in FIG. 2. FIG. 2 shows alarm links in a PON system in the prior art. The PON system provides three types of Operations, Administration and Maintenance (OAM) channels: embedded OAM, Physical Layer OAM (PLOAM), and Operation and Maintenance Center (OMC). In FIG. 2, the Bit Interleaved Parity (BIP) and Remote Defect Indication (RDI) messages are transmitted through embedded OAM bits or bytes, and the Remote Error Indication (REI) and Deactivate (DACT) messages are transmitted in the form of PLOAM messages.
In a traditional PON system, the OLT is interconnected with the ONU directly through an optical splitter. As shown in FIG. 2, in both the upstream and the downstream directions, failure detection is performed for fiber links and reported by raising alarms such as Loss of Signal (LOS) alarms and Loss of Frame (LOF) alarms; and data transmission performance is detected through BIP check and reported by raising alarms such as Signal Degrade (SD) alarms and Signal Fail (SF) alarms. The result of performance monitoring in the downstream direction is returned to the OLT through RDI and REI messages to facilitate the OLT check and failure locating.
With the emergence of the next-generation optical access network, the LR-PON is proposed. The LR-PON needs to reach farther and enable the OLT to cover the ONUs 100 km away. FIG. 3 shows a structure of an LR-PON system in the prior art. As shown in FIG. 3, the LR-PON includes an OLT, a regenerator, more than one ONU, and an ODN1 and an ODN2 which are located on both sides of the regenerator. The ODN1 connects the regenerator to the OLT, and includes a feed fiber. The ODN2 connects the regenerator to the ONU, and includes: a passive optical splitter, a feed fiber between the passive optical splitter and the regenerator, and a branch fiber between the passive optical splitter and the ONU. By adding a regenerator in the LR-PON system, the OLT in the LR-PON system covers the ONUs up to 100 km away. Through an Electrical Relay (E-R) regenerator in the prior art, the coverage of the PON can be extended in E-R mode.
Although the E-R regenerator extends the coverage of the PON and enables the OLT to cover ONUs as far as required, long-distance fiber failures may arise after the fiber transmission distance is extended from 20 km to 100 km. The active E-R device introduced into the PON also reduces the stability and reliability of the device in the system. The E-R regenerator on the feed fiber divides the Fiber path into two sections, which increases the complexity of fast failure locating. The existing PON system provides complete monitoring and maintenance functions and specifies various alarm indications, performance events and management operations between the OLT and the ONU in detail, but such functions are applicable only to the scenarios where the OLT interworks with the ONU directly through optical signals in the traditional PON system. In the E-R LR-PON application, the E-R regenerator does not perform necessary monitoring or processing for the PON signals. Previous alarm indications and maintenance functions are transmitted transparently, and the failures of the intermediate nodes cannot be analyzed or located. Therefore, the existing E-R LR-PON solution does not monitor the LR-PON signals, and does not put forward various alarm indications raised in the LR-PON signal monitoring or the corresponding processing method.